The present invention relates to an antenna device disposed inside a vehicle exterior accessory which is mounted on the exterior of a vehicle body.
Additional parts mounted on a vehicle body, such as spoiler, wing, and bumper, are known as vehicle exterior accessories. Vehicles are further mounted with a transmitter/receiver such as for AM radio, FM radio, television, and GPS. Inventions which improve a vehicle design by disposing a receiving antenna for a radio or the like inside a vehicle exterior accessory such as a spoiler, and wing are known (for example, JP 2012-65184 A and JP 2010-274821 A).
An antenna device includes an antenna element which receives wave signals and an amplifier which amplifies the wave signals received by the antenna element and outputs the amplified signals. In related arts, a ground (GND) is positioned away from an amplifier, resulting in lowered performance of the antenna device. Further, an amplifier is fixed to a vehicle exterior accessory such as a spoiler with a nail-shaped element or the like, while vehicle exterior accessories are fixed to a vehicle body by a fastening bolt. Because vehicle exterior accessories are made of resin, when a vehicle exterior accessory is expanded or contracted by heat, the amplifier is displaced along with the vehicle exterior accessory. Because the fastening bolt does not move, on the other hand, it has been required to provide a spring with a grounding bracket to minimize the distortion due to the heat expansion or contraction.
Further, the amplifiers are required to be waterproof because water such as rain may penetrate into vehicle exterior accessories. In related arts, the amplifiers are molded (resin molding) or sealed with rubber in order to waterproof the amplifier. However, in case of molding, as load is applied to an amplifier substrate by pressure or the like when forming, there is a risk that elements on the substrate may be damaged. As described above, prior arts have a problem of cost increase because of the increase in the number of parts due to required measures for heat expansion or contraction and waterproofing. Further, as a spring is used as measures for heat expansion or contraction, it is necessary to prepare a mounting space for the spring. As a result, there is a risk that types of vehicles which are capable of mounting the antenna device may be limited.
Further, when the amplifier is fixed with a nail-shaped element to a vehicle exterior accessory, the amplifier may be vibrated due to vibrations or the like of the vehicle, resulting in an occurrence of abnormal noise. If a member such as a cushion is provided as measures against such abnormal noise, a problem of manufacturing cost increase arises. Further, because it is possible that a clearance (space) is created between the nail-shaped element and the amplifier due to heat expansion or the like of the vehicle exterior accessory, the amplifier may be caused to come away from the nail-shaped element. This raises a risk of occurrence of abnormal noise or damage in the nail-shaped element.